During oil exploration and extraction, long tubular members, known as pipe strings, are run from a drilling rig into the ground through bore holes so as to extend underground ultimately to an underground oil reservoir. These pipe strings are not continuous, but instead are formed of separate lengths which are connected together. This is not only because of the distances involved making a continuous length of pipe impractical, but also because different operating tools are normally connected within the pipe string to suit requirements—for example if a branch bore needs to be drilled or the like. Each pipe string element is therefore usually formed with a male connector on one end and a matching female connector on the other end (typically a male and female thread), so that the next pipe string element is connected to the end of the previous one by simply inserting one end into the other and then rotating to connect them together.
In practice, however, it is found that, during use, adjacent pipe string elements can rotate relative to each other. For example, for off-shore operations, the pipe string will extend from the drilling rig to the sea bed through the sea and the wave action and vibration in the pipe string resulting therefrom can cause the connected male and female connectors to rotate relative to each other. A relatively small amount of rotation can, then, cause the whole connection to fail.
It is therefore the practice in the art to impose some sort of rotation lock on the connection between pipe string elements which prevents relative rotation between the connected male and female connectors, thereby preventing unintentional release of the joint. For example, one known approach is to deform the joint once the connection is made so that the concentric male and female parts are deformed into an eccentric shape and hence are prevented from relative rotation. Another approach is to form radially extending apertures in the walls of the male and female members which align with each other when the connector is fully made, a pin, screw or the like then being inserted through both holes to prevent rotation between the two connector parts. Other solutions are also known. However, none give a satisfactory solution for a variety of reasons. For example, deforming (crimping) requires additional tools to be used during the connection process, extending the time associated with completing the operation and also taking up valuable space on the rig. Use of locking screws/pins requires very precise manufacturing in order to ensure that the radial apertures are properly aligned when the connection is fully made, thereby increasing cost.
According to the present invention there is provided a tubular pipe string element having: a first end with a male connector formed thereon, a second end having a female connector formed thereon which is complementary to the male connector, said male and female connectors being of the rotational connector type such that, in use, the male connector is engageable in a female connector of another pipe string element and rotatable relative thereto in a first direction in order to secure the connection and in a second direction in order to release the connection, and complementary anti-rotation devices associated with said male and female connectors which anti-rotation devices cooperate to prevent unintentional relative rotation between male and female connectors in the second direction; wherein said anti-rotation devices comprises: at least one saw-tooth profiled, radially extending tooth having a shallow leading tooth flank angle facing in one of said first and second direction and a steep trailing tooth flank angle facing in the other of said first and second directions formed on the pipe string element proximate one end thereof in association with one of the male and female connectors, and at least one detent member formed on the pipe string element proximate the other end thereof in association with the other of the male and female connectors, said at least one saw-tooth profiled tooth and said at least one detent member being rotationally and axially fast, with the pipe string element wherein, in use upon relative rotation in the first direction between engaged male and female connectors, the leading flank of the at least one saw-tooth profiled tooth engages with the at least one detent member, urging it to retract against a biasing member and allowing the connectors to rotate into a fully connected position, the steep trailing tooth flank being trapped by the detent member when in the fully connected position so as to prevent unintentional release of the connection.
A pipe string element in accordance with the invention has the advantage that the anti-rotation elements operate to prevent unintentional disconnection of the male and female connectors without requiring any additional tooling during the making up of the tool string and also without causing any permanent damage or deformation to either of the pipe string components, making the components more easily reused.
Preferably, each detent member comprises a cantilever spring arm provided on the relevant surface of the male or female connector with a locking member thereon which is urged by the spring force of the spring arm into the rotational path of the saw-tooth profiled tooth but which is retractable out of said path against the spring force upon engagement with the leading flank of the at least one tooth. In a particularly preferred embodiment, a through opening is formed in the wall of the tubular member in which the locking member engages. This can be achieved particularly effectively by forming the spring arm integrally with the pipe string element by cut outs in the wall of the pipe string element. This has the advantage that the locking member and/or spring arm is accessible from the side of the pipe string element remote from the mating connectors, thereby facilitating manual retraction of the locking member in order to release the connectors.
The male and female connectors are preferably threaded connectors but other types of rotational connector are also possible such as bayonet connectors.
The anti-rotation elements are preferably located proximate a tip end of the female connector and proximate the root end of the male connector. In the preferred embodiment, the at least one tooth is provided on the outer surface of the male connector and the at least one locking member and associated spring arm is provided in the tubular wall of the female connector. In this way, the manual release of the locking member can be achieved from outside of the pipe string element using a specially designed release tool.
Preferably, a plurality of spring arms and associated locking members are provided, which may be equi-angularly distributed around the pipe string element but may also be distributed otherwise there-around, with a corresponding plurality of teeth also being provided. The teeth may then be provided around the entire periphery of the string element or may be provided in distinct groups, the groups being distributed around the pipe string element to match the distribution of the locking members.
In a particularly preferred embodiment, the trailing edge of each saw-tooth profiled tooth is inclined backwards to form an undercut, and the trailing face of the locking member which engages against the trailing flank to prevent release is similarly undercut in a complementary manner so that the surfaces hook into each other to provide a particularly secure block against unintentional release.